The disclosure of Japanese Patent Application No. 2002-344564 filed on Nov. 27, 2002, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to fuel injection amount control method and apparatus of an internal combustion engine, and, more particularly, to apparatus and method of controlling a fuel injection amount so that the air/fuel ratio can be kept substantially constant even during transient operations of the engine.
2. Description of Related Art
In an internal combustion engine of an electronically-controlled fuel injection type, fuel is supplied to each of cylinders of the engine through fuel injection immediately before the suction stroke of the cylinder or during the suction stroke. The cylinder that currently needs to be supplied with the fuel will be hereinafter called xe2x80x9cfuel injection cylinderxe2x80x9d. This type of the engine is required to calculate an amount of intake air drawn into the fuel injection cylinder during the suction stroke, and inject fuel in an amount matching the calculated intake air amount by the time when a corresponding intake valve is closed at the end of the suction stroke (i.e., by a point in time when the intake valve shifts from an open state to a closed state) at the latest. In some cases, the fuel needs to be injected prior to a start of the suction stroke.
To meet the above requirements, a control apparatus of an internal combustion engine as disclosed in, for example, U.S. Pat. No. 6,014,955 estimates an opening angle of a throttle valve as one of operating state quantities of the engine up to the time of closing of the intake valve of the fuel injection cylinder, and estimates an amount of intake air that will be present in the fuel injection cylinder at the time of closing of the intake valve, based on at least the estimated throttle opening and an air model that models the behavior of air in the intake system of the engine, at a point in time prior to the time of closing of the intake valve. The control apparatus then generates a command to inject fuel into the cylinder in an amount that matches the estimated intake air amount.
The conventional control apparatus as described above may suffer from the following problem: if a difference (or estimation error) arises between the estimated intake air amount and the actual intake air amount, for example, due to a difference between the estimated throttle opening and the actual throttle opening, the control apparatus, which is not provided with a means for compensating for the estimation error, cannot produce an appropriate value of the fuel injection amount, and the air/fuel ratio may fluctuate or deviate from a target value.
In the case where the conventional control apparatus is provided with a general feedback controller for performing feedback control so as to compensate for the estimation error, a feedback control system is desirably constructed so that feedback control constants, such as a proportional gain and an integration gain, used by the controller need not be frequently changed in response to frequently varying operating conditions (e.g., the engine speed and the temperature) of the engine, thereby making the feedback controller simple in construction.
It is therefore an object of the invention to provide a fuel injection amount control method and a fuel injection amount control apparatus, which use a feedback controller having a simple construction or arrangement, for promptly compensating for an estimation error in the intake air amount, thereby to promptly make the air/fuel ratio stable particularly during a transient engine operation, e.g., upon a sudden change of the throttle opening.
To accomplish the above and/or other object(s), there is provided according to a first aspect of the invention a method of controlling a fuel injection amount of an internal combustion engine with respect to a suction stroke for which fuel is injected, comprising the steps of (a) estimating an operating state quantity of the engine to be established at the time of closing of an intake valve in the suction stroke in question, at a point in time prior to the time of closing of the intake valve, (b) estimating an intake air amount in the suction stroke based on the estimated operating state quantity, (c) calculating, as a pre-correction estimated necessary fuel amount, a provisional fuel amount that is needed along with the estimated intake air amount to achieve a target air/fuel ratio, (d) calculating an actual necessary fuel amount as an amount of fuel actually needed for achieving the target air/fuel ratio in a previous suction stroke that precedes the suction stroke in question, based on a known value of the operating state quantity, at a point in time after closing of the intake valve in the previous suction stroke, (e) calculating an actual intake fuel amount as an amount of fuel actually inducted into a cylinder of the engine during the previous suction stroke, based on at least an amount of fuel actually injected for the previous suction stroke, (f) determining an excess or shortage of the fuel in the previous suction stroke based on the calculated actual necessary fuel amount and the calculated actual intake fuel amount, and calculating a fuel feedback correction amount corresponding to the determined excess or shortage of the fuel, (g) calculating a normal estimated necessary fuel amount by correcting the pre-correction estimated necessary fuel amount with the calculated fuel feedback correction amount, (h) calculating a fuel injection amount based on at least the calculated normal estimated necessary fuel amount, and (i) injecting the fuel having the calculated fuel injection amount for the suction stroke in question, at a point in time before the time of closing of the intake valve in the suction stroke.
The above-mentioned xe2x80x9csuction stroke in questionxe2x80x9d may refer to the present suction stroke in which the cylinder for which the fuel injection amount is controlled according to the above method is currently placed, or to the coming suction stroke of the cylinder, namely, the suction stroke into which the cylinder comes next. In the method according to the above aspect of the invention, the xe2x80x9csuction stroke in questionxe2x80x9d, xe2x80x9cprevious suction strokexe2x80x9d and the xe2x80x9csecond previous suction strokexe2x80x9d may be the current or coming, previous and second previous suction strokes with respect to a particular cylinder that is an arbitrarily selected one of the cylinders provided in the engine, or may be the current or coming, previous and second previous suction strokes with respect to a non-particular cylinder for which fuel injection is performed next, out of the cylinders of the engine that successively enter the suction stroke.
In the fuel injection amount control method as described above, the amount of intake air that will be present in the cylinder at the time of closing of the intake valve in the suction stroke in question is estimated based on the estimated operating state quantity (e.g., an opening angle of a throttle valve), at a point in time earlier than the time of closing of the intake valve. Then, the pre-correction estimated necessary fuel amount is calculated as a provisional amount of fuel needed for achieving the target air/fuel ratio (e.g., the stoichiometric air/fuel ratio) if the estimated intake air amount is actually provided. Namely, the pre-correction estimated necessary fuel amount is calculated based on the estimated intake air amount and the target air/fuel ratio. Accordingly, the pre-correction estimated necessary fuel amount is influenced by an estimation error in the estimated intake air amount.
In the meantime, since the operating state quantity established at the time of closing of the intake valve in the previous suction stroke is known after closing of the intake valve in the previous suction stroke, the actual intake air amount in the previous suction stroke can be determined from the known operating state quantity. It is therefore possible to accurately determine the actual necessary fuel amount as the amount of fuel actually needed for making the air/fuel ratio of an air-fuel mixture in the cylinder equal to the target air/fuel ratio in the previous suction stroke. On the other hand, since the amount of fuel actually injected for the previous suction stroke is known after closing of the intake valve in the previous suction stroke, the actual intake fuel amount as an amount of fuel actually drawn into the cylinder during the previous suction stroke can be accurately determined based on at least the known fuel injection amount for the previous suction stroke.
In the fuel injection amount control method according to the above aspect of the invention, an excess or shortage of fuel in the previous suction stroke is calculated based on a difference between the actual necessary fuel amount and the actual intake fuel amount that are determined in the above-described manners, and the fuel feedback correction amount is calculated so as to compensate for the excess or shortage of the fuel. Subsequently, the normal estimated necessary fuel amount is calculated by correcting the pre-correction estimated necessary fuel amount with the fuel feedback correction amount, and the fuel injection amount is calculated based on at least the normal estimated necessary fuel amount. Accordingly, the excess or shortage of the fuel that occurs in the previous suction stroke is compensated for or eliminated in the present or coming suction stroke, and therefore the air/fuel ratio can be promptly stabilized and kept stable with high accuracy.
Also, the fuel injection amount is calculated based on the normal estimated necessary fuel amount resulting from correction using the fuel feedback correction amount. Accordingly, even in the case where the calculated fuel injection amount differs from the normal estimated necessary fuel amount by an amount that depends upon an operating state of the engine, such as the case where the fuel injection amount is calculated based on the normal estimated necessary fuel amount in view of the (actual) fuel deposition amount that varies depending upon the operating state of the engine as described later, the fuel of the normal estimated necessary fuel amount that surely reflects the fuel feedback correction amount is accurately drawn into the fuel injection cylinder, irrespective of the operating state of the engine, if the fuel of the calculated fuel injection amount is injected. Accordingly, feedback control constants, such as a proportional gain, used by a feedback controller for calculating the fuel feedback correction amount need not be changed depending upon the frequently varying operating state of the engine, and therefore the feedback controller can be made simple in construction.
According to a second aspect of the invention, there is provided an apparatus for controlling a fuel injection amount of an internal combustion engine including a fuel injector that injects a fuel in response to a command, with respect to a suction stroke for which the fuel is injected, which apparatus includes an operating state quantity estimating unit, operating state quantity acquiring unit, estimated intake air amount calculating unit, pre-correction estimated necessary fuel amount calculating unit, actual intake air amount calculating unit, actual necessary fuel amount calculating unit, actual intake fuel amount calculating unit, fuel feedback correction amount calculating unit, normal estimated necessary fuel amount calculating unit, fuel injection amount calculating unit and a fuel injection commanding unit. In the following, the function of each unit will be described.
The operating state quantity estimating unit estimates an operating state quantity of the engine to be established at a point in time that is later than the present time. The operating state quantity acquiring unit acquires an actual operating state quantity of the engine established at a point in time that is earlier than the present time. A typical example of the operating state quantity is an opening angle of a throttle valve.
The estimated intake air amount calculating unit calculates an estimated intake air amount as an amount of intake air that will be present in the cylinder at the time of closing of the intake valve in the current or coming suction stroke, at a first predetermined point in time that is earlier than the time of closing of the intake valve in this suction stroke. The estimated intake air amount is calculated based on the operating state quantity to be established at a point in time later than the first predetermined point, which quantity is estimated by the operating state quantity estimating unit, and an air model that models the behavior of air in the intake system of the engine. Namely, with regard to the cylinder that is about to enter the suction stroke (or has ready entered the suction stroke), the estimated intake air amount calculating unit estimates the intake air amount of this cylinder for the time of closing of the intake valve, at the first predetermined point that is earlier than the time at which the intake valve of the cylinder shifts from the open state to the closed state in the coming or present suction stroke (i.e., the time of closing of the intake valve).
The pre-correction estimated necessary fuel amount calculating unit calculates a pre-correction estimated necessary fuel amount as a provisional amount of fuel needed in the current or coming suction stroke, based on the estimated intake air amount, at a second predetermined point in time that is later than the first predetermined point and is earlier than the time of closing of the intake valve in this suction stroke. For example, the pre-correction estimated necessary fuel amount calculating unit may calculate the pre-correction estimated necessary fuel amount by dividing the estimated intake air amount by a target air/fuel ratio that is separately determined according to the operating state of the engine, or a predetermined air/fuel ratio.
The actual intake air amount calculating unit calculates an actual intake air amount as an amount of intake air that was actually present in the cylinder at the time of closing of the intake valve in a previous suction stroke that precedes the current or coming suction stroke, at a third predetermined point in time that is later than the time of closing of the intake valve in the previous suction stroke and is earlier than the time of closing of the intake valve in the current or coming suction stroke. The actual intake air amount is calculated based on the actual operating state quantity acquired by the operating state quantity acquiring unit and the air model. Since the third predetermined point is later than closing of the intake valve in the previous suction stroke, the operating state quantity used for calculating the actual intake air amount for the time of closing of the intake valve in the previous suction stroke is already known at this point and can be thus acquired by the operating state quantity acquiring unit. Thus, the actual intake air amount can be accurately determined based on the known operating state quantity and the air model.
The actual necessary fuel amount calculating unit calculates an actual necessary fuel amount as an amount of fuel actually needed in the previous suction stroke, based on the calculated actual intake air amount, at a fourth predetermined point in time that is later than the third predetermined point and is earlier than the time of closing of the intake valve in the current or coming suction stroke. For example, the actual necessary fuel amount calculating unit calculates the actual necessary fuel amount by dividing the actual intake air amount by the target air/fuel ratio, in a similar manner to the pre-correction estimated necessary fuel amount calculating unit.
The actual intake fuel amount calculating unit calculates an actual intake fuel amount as an amount of fuel actually inducted into the cylinder during the previous suction stroke, at a fifth predetermined point in time that is earlier than the time of closing of the intake valve in the current or coming suction stroke, based on at least an amount of fuel actually injected for the previous suction stroke. In this case, the actual intake fuel amount is preferably determined in view of the actual fuel deposition amount, as described later.
The fuel feedback correction amount calculating unit calculates a fuel feedback correction amount based on the calculated actual necessary fuel amount and the calculated actual intake fuel amount, at a sixth predetermined point in time that is later than the fourth and fifth predetermined points and is earlier than the time of closing of the intake valve in the current or coming suction stroke.
For example, since a difference between the calculated actual necessary fuel amount and the calculated actual intake fuel amount represents an excess or shortage of fuel in the previous suction stroke, the fuel feedback correction amount for compensating for the excess or shortage of the fuel is calculated by using the difference between the actual necessary fuel amount and the actual intake fuel amount, and a controller, such as a proportional-integral controller, that receives this difference as an input value.
The normal estimated necessary fuel amount calculating unit calculates a normal estimated necessary fuel amount as a normal fuel amount needed for the current or coming suction stroke, by correcting the calculated pre-correction estimated necessary fuel amount with the fuel feedback correction amount, at a seventh predetermined point in time that is later than the second and sixth predetermined points and is earlier than the time of closing of the intake valve in the current or coming suction stroke.
The fuel injection amount calculating unit calculates a fuel injection amount as an amount of fuel to be injected from the fuel injector for the current or coming suction stroke, based on at least the calculated normal estimated necessary fuel amount, at an eighth predetermined point in time that is later than the seventh predetermined point and is earlier than the time of closing of the intake valve in this suction stroke. In this case, the fuel injection amount calculating unit is preferably arranged to calculate the fuel injection amount so that, if the fuel of the calculated fuel injection amount is injected, the fuel of the normal estimated necessary fuel amount is inducted or drawn into the cylinder (fuel injection cylinder) during the current or coming suction stroke. Furthermore, it is preferable to determine the fuel injection amount in view of the actual fuel deposition amount, as described later.
The fuel injection commanding unit generates a command to inject the fuel having the calculated fuel injection amount, to the fuel injector, at a ninth predetermined point in time that is later than the eighth predetermined point and is earlier than the time of closing of the intake valve in the current or coming suction stroke. With the command thus generated, the fuel of the fuel injection amount is injected from the fuel injector.
The fuel injection amount control apparatus according to the above aspect of the invention repeatedly executes the above-described process for each suction stroke (with respect to each cylinder) so that an excess or shortage of the fuel that occurs in the previous suction stroke is immediately reflected (namely, compensated for) by the fuel injection amount for the coming and subsequent suction strokes. Accordingly, the air/fuel ratio can be kept at a stable value. Also, if the fuel is injected in the calculated fuel injection amount, the fuel of the normal estimated necessary fuel amount that surely reflects the fuel feedback correction amount is precisely inducted or drawn into the fuel injection cylinder, without regard to the operating state of the engine. Therefore, feedback control constants used for calculating the fuel feedback correction amount need not be changed depending upon the frequently varying operating conditions of the engine. Consequently, the feedback controller for calculating the fuel feedback correction amount can be made simple in construction.
In one preferred embodiment of the invention, the fuel injection amount control apparatus further includes an actual fuel deposition amount calculating unit that calculates an actual fuel deposition amount, and the actual intake fuel amount calculating unit calculates the actual intake fuel amount by using a forward model of the fuel behavior model, in view of the actual fuel deposition amount, while the fuel injection amount calculating unit calculates the fuel injection amount by using a reverse model of the fuel behavior model, in view of the calculated actual fuel deposition amount.
With the above arrangement, the fuel injection amount is determined while taking account of the fuel deposition amount that changes depending upon the operating state of the engine. Accordingly, an appropriate fuel injection amount is calculated for the fuel injection cylinder, and the air/fuel ratio can be made further stable.
More specifically, the actual fuel deposition amount calculating unit calculates an actual fuel deposition amount as an amount of fuel deposited after a particular suction stroke and before a suction stroke that comes next to the particular suction stroke, based on a fuel injection amount that is actually injected for the particular suction stroke, an actual fuel deposition amount as an amount of fuel deposited after a suction stroke that precedes the particular suction stroke and before the particular suction stroke, and the above-described fuel behavior model.
Namely, the actual fuel deposition amount calculating unit calculates a new actual fuel deposition amount (i.e., an amount of fuel deposited after the particular suction stroke), based on the amount of fuel deposited in the intake system, out of the amount of fuel actually injected for the particular suction stroke, and an amount of fuel remaining in the intake system, out of the actual amount of fuel deposited in the intake system before the particular suction stroke.
The actual intake fuel amount calculating unit calculates the actual intake fuel amount as an amount of fuel actually inducted into the cylinder during the previous suction stroke, based on a forward model of the fuel behavior model. The actual intake fuel amount is calculated from an amount of fuel actually inducted into the cylinder during the previous suction stroke, out of an amount of fuel actually injected for the previous suction stroke, and an amount of fuel actually inducted into the cylinder during the previous suction stroke, out of the actual fuel deposition amount calculated by the actual fuel deposition amount calculating unit as an amount of fuel actually deposited after a second previous suction stroke that precedes the previous suction stroke and before the previous suction stroke.
Namely, the actual intake fuel amount calculating unit calculates the sum of a portion of the actual fuel injection amount for the previous suction stroke, which portion is inducted into the fuel injection cylinder, and a portion of the actual amount of fuel deposited before the previous suction stroke, which portion is inducted into the fuel injection cylinder, as the intake fuel amount as the amount of fuel actually inducted into the cylinder during the previous suction stroke.
The fuel injection amount calculating unit calculates the fuel injection amount based on a reverse model of the fuel behavior model so that a sum of an amount of fuel to be inducted into the cylinder during the current or coming stroke, out of the fuel injection amount to be injected for this suction stroke, and an amount of fuel to be inducted into the cylinder during this suction stroke, out of the fuel deposition amount calculated by the actual fuel deposition amount calculating unit as an amount of fuel actually deposited after the previous suction stroke and before the current or coming suction stroke becomes equal to the calculated normal estimated necessary fuel amount.
Namely, the fuel injection amount calculating unit calculates the amount of fuel that should be injected from the fuel injector so that the normal estimated necessary fuel amount is inducted or drawn into the fuel injection cylinder, while taking account of a portion of the fuel injection amount that is inducted into the cylinder without adhering to the intake system, and a portion of the actual amount of fuel deposited before the current or coming suction stroke, which portion is inducted into the cylinder. The thus calculated injection amount is set as the fuel injection amount for the current or coming suction stroke.
With the above arrangement, the actual intake fuel amount is accurately calculated in view of the actual fuel deposition amount calculated with high accuracy based on the actual fuel injection amount. Thus, an excess or shortage of the fuel inducted into the cylinder is precisely determined, and the thus determined excess or shortage is reflected by the feedback correction amount, thus permitting the air/fuel ratio to be stable. Also, since the fuel injection amount is calculated in view of the actual fuel deposition amount calculated with high accuracy, a fuel whose amount is extremely close to the actual necessary fuel amount (i.e., the pre-correction estimated necessary fuel amount or normal estimated necessary fuel amount) is supplied to the fuel injection cylinder through injection of the fuel of the calculated fuel injection amount in the case where no estimation error is present in the intake air amount (i.e., where the fuel feedback correction amount is equal to zero). This also contributes to stabilization of the air/fuel ratio for each suction stroke.
In the case where the actual intake fuel amount calculating unit is arranged to calculate the actual intake fuel amount by using the forward model of the fuel behavior model in view of the actual fuel deposition amount, and the fuel injection amount calculating unit is arranged to calculate the fuel injection amount by using the reverse model of the fuel behavior model in view of the actual fuel deposition amount, it is preferable that the actual intake fuel amount calculating unit determines a fuel deposition rate and a fuel remaining rate used by the forward model of the fuel behavior model, based on the actual intake air amount for the time of closing of the intake valve in the previous suction stroke, and that the fuel injection amount calculating unit determines a fuel deposition rate and a fuel remaining rate used by the reverse model of the fuel behavior model, based on the estimated intake air amount.
With the above arrangement, the fuel deposition rate and the fuel remaining rate used by the actual intake fuel amount calculating unit in the forward model of the fuel behavior model are determined based on the actual intake air amount at the time of closing of the intake valve in the previous suction stroke, which is determined based on the operating state quantity that is known after closing of the intake valve in the previous suction stroke and the air model. Thus, the deposition rate and the remaining rate accurately represent the actual behavior of the fuel in the intake system of the engine. Accordingly, the actual intake fuel amount is calculated with further improved accuracy.
Also, the fuel deposition rate and the fuel remaining rate used by the fuel injection amount calculating unit in the reverse model of the fuel behavior model are determined based on the estimated intake air amount to be established at the time of closing of the intake valve in the present or coming suction stroke, which amount is determined based on the operating state quantity estimated by the operating state quantity estimating unit and the air model. Thus, the deposition rate and the remaining rate accurately represent the behavior of the fuel in the intake system of the engine, which is estimated for the time of closing of the intake valve in the present or coming suction stroke. Accordingly, the fuel injection amount that would result in induction of the fuel of the normal estimated necessary fuel amount into the fuel injection cylinder is calculated with further improved accuracy.
In another preferred embodiment of the fuel injection amount control apparatus as described above, the fuel feedback correction amount calculating unit calculates the fuel feedback correction amount based on at least a time integral value of a difference between the calculated actual necessary fuel amount and the calculated actual intake fuel amount, and the estimated intake air amount calculating unit and the actual intake air amount calculating unit are constructed such that, when the internal combustion engine is in a steady operating state, the estimated intake air amount calculated by the estimated intake air amount calculating unit and the actual intake air amount calculated by the actual intake air amount calculating unit become substantially equal to each other.
With the above arrangement, when the engine is in a steady operating state, the estimated intake air amount and the actual intake air amount become equal to each other, and therefore the pre-correction estimated necessary fuel amount calculated based on the estimated intake air amount becomes equal to the actual necessary fuel amount calculated based on the actual intake air amount. Accordingly, each time the engine is kept in a steady operating state for a predetermined period of time or longer, it is guaranteed that the time integral value of the difference between the calculated actual necessary fuel amount and the calculated actual intake fuel amount becomes equal to zero.
The above-indicated time integral value of the difference corresponds to a time integral value of an excess or shortage of the fuel. Accordingly, each time the engine returns to a steady operating state after shifting from a steady operating state to a transient operating state in which an excess or shortage of fuel is likely to occur, it is guaranteed that the time integral value of the excess or shortage of the fuel becomes equal to zero. Consequently, the average air/fuel ratio in a period in which the engine once shifts from the steady operating state to the transient operating state and then returns to the steady operating state (namely, the total intake air amount in this period/the total fuel (injection) amount in this period) can be made equal to a certain target air/fuel ratio (e.g., the stoichiometric air/fuel ratio).
Generally, a three-way catalyst having the function of storing and releasing oxygen is often mounted in the exhaust system of the engine, for purifying exhaust gas having an air/fuel ratio that deviates from the stoichiometric air/fuel ratio by a certain degree. The three-way catalyst performs the oxygen storage/release function with high efficiency when the amount of oxygen stored in the catalyst is kept at around a predetermined amount (for example, about a half of the maximum oxygen storage amount of the catalyst). Meanwhile, the oxygen storage amount of the three-way catalyst decreases when the air/fuel ratio of the exhaust gas flowing into the catalyst is rich, and increases when the air/fuel ratio of the exhaust gas is lean. Accordingly, if the average air/fuel ratio within the above-described period is equal to the target air/fuel ratio (e.g., the stoichiometric air/fuel ratio), the oxygen storage amount of the three-way catalyst does not change over the above-described period. Consequently, the oxygen storage amount of the catalyst can be maintained in the vicinity of the predetermined amount.
As is understood from the above description, where the three-way catalyst having the function of storing and releasing oxygen is mounted in the exhaust system of the engine, the oxygen storage/release function of the three-way catalyst does not deteriorate even in the case where the engine once shifts from the steady operating state to the transient operating state and then returns to the steady operating state. Thus, an otherwise possible increase in the amount of emissions of the exhaust gas can be prevented or suppressed.
In the fuel injection amount control apparatus as described above, the ninth predetermined point is actually required to be a point in time that is earlier than the time of closing of the intake valve by a period of time that is the sum of the time needed for fuel injection and the time needed for the injected fuel to be drawn into the cylinder. In the case of an internal combustion engine of in-cylinder or direct injection type, or in the case where the flow rate at which the fuel is injected by the fuel injector is considerably large, however, the ninth predetermined point may be any point in time prior to the time of closing of the intake valve. The ninth predetermined point may also be a point in time after a start of fuel injection.